The present invention relates generally to container closures and more particularly to a closure having internal threads for engagement with external threads of a container.
Various types of closures are presently made for threaded engagement with container necks. It is well known for a closure to be molded from plastic and to include a top wall and an internally threaded annular side wall depending therefrom.
Such closures typically include a seal to engage a rim at the top of the container neck. To obtain a satisfactory seal, pressure must be exerted upon the rim of the container neck by the seal. This pressure creates friction between the closure and the container neck which may make removal of the closure difficult.
Closures of this type are generally intended to be removed manually by gripping the side wall of the closure and twisting it relative to the container. To facilitate removal of the closure, the closure may have vertical ribs or the like disposed about its periphery on the side wall. However, some persons, such as arthritics, may be unable to comfortably grip the side wall and rotate the cap due to reduced strength and dexterity of their hands. In the past, such persons have commonly had to use tools or specialized devices to open containers sealed with conventional closures. There has been a need for a closure which may be rotated by a person with reduced manual dexterity without the use of such devices.
In providing an acceptable seal for a closure, the closure may be provided with a separately formed seal element of plastisol or a coated liner board. Alternatively, some closures are formed with an internal integral sealing rib and are termed linerless closures. With a closure having a separately formed liner, the latter is inserted as a separate piece against the lower surface of the top wall of the closure. Liners are commonly inserted by inverting the closure and pressing the liner downwardly into place against the upwardly facing lower surface of the top wall. To facilitate such insertion without requiring a specially configured surface to support the closure, it is desirable that a closure be capable of maintaining a stable mechanical equilibrium in an inverted position on a flat horizontal surface.
Another desirable feature in closures is to avoid having portions extending outwardly beyond the side wall. Where portions project radially outwardly beyond the side wall, there may be interference between adjacent closures when a plurality of closures are disposed side-by-side adjacent one another. This may also interfere with handling of the closures by conventional capping equipment.